First of all, you're welcome back to Steemit, you're right a lot has changed, so club5050 means that if you transfer out 50 Steems tokens from your account within a month, you must also power up at least 50 Steems too (whatever you transfer out of your account within a month, you must also power up same or more). Club75 have a 2-month accounting period, and this means you must power up 3x of your transfer out within 2 months, for example, if you transfer out 25 tokens, then you must power up 75 tokens. Lastly, club100 means you must power up all the rewards you receive consecutively for 3 months to join and thereafter. Yes accounting period of club100 is 3 months.

Clubstatus encouraged power-up culture and has helped many of us to build our (Steem power) account. It's a nice initiative.